The present invention relates generally to springs. More particularly, the present invention relates to multihelical springs.
Springs are used extensively in many industries for their dynamic and mechanical properties. For example, large scale springs are used in the automotive industry, or smaller scale springs are used for smaller electronic and/or mechanical devices. Steel springs have been often used in light of their quality of fabrication, stiffness, strength, and their ability to be mass produced. However, steel springs tend to be relatively heavy, and disadvantageous to use in certain applications given their weight. For example, in applications such as automobiles, airplanes, and railway cars, it is critical to reduce the weight of various components to reduce the overall weight of the apparatus. Other drawbacks of steel springs are that they have limited corrosion resistance, fatigue strength, have a high coefficient of thermal expansion, have magnetic properties, and are electrically conductive.
One approach to some of the drawbacks of steel springs is to form single helical springs from composite materials. Single helical springs formed of composite materials have been developed, to take advantage of light weight characteristics of plastic materials. However, these types of springs fail to provide sufficient stiffness to replace steel springs. A single helical spring is a torsion bar wrapped into a helical form, and the stiffness of a torsion bar is determined by the shear modulus of elasticity of the material. As the shear modulus of composite materials is much smaller than the shear modulus of steel, the stiffness of a single helical composite spring is much less than that of a steel single helical spring.
Accordingly, what is needed is a lightweight spring capable of providing sufficient stiffness for a wide variety of applications. What is further needed is a spring which has an improved resistance to fatigue and corrosion.
A helical spring includes one or more layers of material distributed in a first helical coiled configuration, the first helical coiled configuration extending from a first end to a second end and wound in a first direction. The helical spring further includes one or more layers of material distributed in a second helical coiled configuration, the second helical coiled configuration extending from one end to another end in a second direction. Each layer of the first helical coiled configuration overlies a layer of the second helical coiled configuration at multiple intersections to form a single spring unit.
Several options for the spring are as follows. For instance, in one option, the material comprises composite material. In another option, the composite material comprises a polymer impregnated with multiple fibers, for example, carbon fibers. In another option, the first helical coil configuration and the second helical coil configuration are interwoven together. In yet another option, each layer is bonded together.
In another embodiment, a helical spring a multi-helical unit includes a number of layers of composite material disposed in a multi-helical configuration. The multi-helical unit includes layers of at least a first strand, a second strand, a third strand, and a fourth strand of composite material. The first strand is disposed in a first coiled configuration, the second strand is disposed in a second coiled configuration, the third strand is disposed over the first strand and the second strand. The third strand disposed in the first coiled configuration, the fourth strand is disposed over the first strand, second strand, and third strand, and the fourth strand disposed in the second coiled configuration. The first strand, the second strand, the third strand, and the fourth strand bonded together in a single spring unit.
Several options for the helical spring are as follows. For instance, in one option, the first strand, second strand, third strand, and fourth strand comprise a single strand of composite material. In another option, the helical spring further includes a fifth strand and sixth strand of composite material, where the fifth strand disposed in a third coiled configuration between the second strand and the third strand, and the sixth strand disposed in the third coiled configuration over the fourth strand of composite material. The composite material optionally comprises polymer material reinforced with a plurality of fibers.
In yet another embodiment, a helical spring includes at least a first set of layers of composite material distributed in a first coiled configuration, the first coiled configuration extending from a first end to a second end. The helical spring further includes at least a second set of layers of composite material distributed in a second coiled configuration, the second coiled configuration extending from one end to another end. The first set of layers and the second set of layers are interwoven together in a crisscross configuration, each layer of the first set of layers overlies a layer of the second set of layers at multiple intersections to form a single spring unit. In addition, the composite material for the first set of layers and the second set of layers comprises a polymer matrix reinforced with a plurality of fibers.
Several options for the helical spring are as follows. For instance, in one option, the helical spring further includes a third set of layers of composite material distributed in a third coiled configuration, where the third set of layers are interwoven with the first set of layers and the second set of layers to form a single spring unit. In another option, the second coiled configuration is offset about 120 degrees from the first coiled configuration, and the third coiled configuration is offset about 120 degrees from the second coiled configuration. In yet another option, the composite material comprises about 30-40% volume of polymer matrix, and about 70-60% volume fiber material, respectively.
In yet another embodiment, a method for forming a spring includes winding m strands of material to form a first layer of composite material in a first helical configuration around a mandrel, winding p strands of material to form a second layer of the composite material coil around the first layer in a second helical configuration, and repeating forming the first layer in the first helical configuration and forming the second layer in the second helical configuration n number of times. The method further includes coupling the layers of material together to form a single spring unit.
Several options for the method are as follows. For instance, in one option, the method further includes winding the first helical configuration in an opposite direction than the second coil. In another option, the method further includes winding a third layer of q strands of material in a third helical configuration around the first layer and the second layer, and repeating winding the first layer in the first helical configuration, winding the second layer in the second helical configuration, and winding the third layer in the third helical configuration n number of times.
Further options include embedding fiber in a polymer prior to winding the first layer and the second layer, or winding the first layer around the mandrel and winding the second layer around the first layer includes continuously winding a single strand of composite material. In yet another option, coupling the layers together includes heating the single spring unit and/or applying pressure to the single spring unit, or curing the single spring unit to form a substantially rigid spring. Still further, in another option, the method further includes decreasing one or more dimensions of the mandrel, and removing the single spring unit from the mandrel. In yet another option, winding the m strands of material and winding the p strands of material comprises winding one or more strands of composite material.
In yet another embodiment, a method for forming a spring includes winding a first layer of a single strand of composite material in a first helical configuration around a mandrel, winding a second layer of the single strand of composite material coil around the first layer in a second helical configuration, winding a third layer of the single strand of composite material in a third helical configuration around the first layer and the second layer, and repeating winding the first layer in the first helical configuration, winding the second layer in the second helical configuration, and winding the third layer in the third helical configuration n number of times. The method further includes coupling the layers of the single strand of composite material together to form a single spring unit.
Several options are as follows. For instance, in one option, the method further includes heating and applying pressure to the single spring unit. In another option, the method further includes reinforcing a polymer with a plurality of fibers to form the composite material. Still further, in another option, winding the first layer includes winding along a first longitudinal direction, and winding the second layer includes winding along a second longitudinal direction, and the first longitudinal direction is opposite the second longitudinal direction.
The spring design allows for use of a lightweight material, without compromising strength or stiffness. The use of composite materials, in conjunction with multi-helical coils, provides for axial stiffness comparable to that of steel. The spring assembly provides for further benefits such as fatigue resistance, high corrosion resistance, and use of optional non-conductive materials.
These and other embodiments, aspects, advantages, and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims and their equivalents.